Null is a typeof Object
* a=null; typeof a – returns object instead of null, it was a bug in early versions of JS but its not fixed in newer versions bcos it breaks backward compatibility and many web applications will break.

Type Coercion: As JS was introduced to be friendly language with developers and they did type conversion of variables used in the expression and this lead to many confusions and later they fixed it but because of backward compatibility we still live with them. One such issue is ‘==’

double equals == and triple equals ===

12 + “4” -> results in “124” because it looks at expression and finds one is string and other is number and hence coerce number into string so that it can do string concatenation
* JS does a lot of type coercion and hence the behavior is unpredictable lot of times, beware of it

Objects in Javascript are free form which means that we can add/remove fields and methods whenever we want. They are not bound to a particular class (like in Java, in fact there is no class concept in JS).

Easiest way to create a object is object inline like – “var obj = {};” Objects can also be created via object literal

Properties and Access Specifiers
All properties within object are public as they dont come with any access specifier. Properties of an object can be accessed in 2 ways
– Using dot notation
– Using square bracketsWhen to use dot notation vs square brackets?

Javascript is created in early 90s by Brendan Eich at Netscape and is later introduced as a standard specification by ECMA committee. Current version supported by most browsers is ECMA5 and newly released version is ECMA 2015 aka ECMA6

Javascript is a lightweight, interpreted or JIT compiled programming language with first class functions.
It is a prototype based, multi-paradigm, dynamic language, scripting language, supporting object oriented, imperative, declarative and functional programming styles. There are lot of buzz words, and we will see each one of them

Lightweight: It has very less foot print in the machine that its running

Interpreted: We do not explicitly compile JS programs (like we do in JAVA, instead its compiled on the go)

First Class Functions: Functions are first class citizens in JS which means

we can assign functions to variables

we can pass functions as method params

we can return a function as a return type from a method

Multi Paradigm: It can support all programming paradigms

Object Oriented: model state and behavior around objects to do sth

Imperative: step by step instructions on HOW TO DO sth (like C)

Declarative: we tell WHAT TO DO rather than HOW TO DO (like scala)

Functional: subset of declarative language style (scala)

Dynamic Language: Method binding to a object is done at runtime rather than at the compile time and during compilation time, compiler wont report (for example, like Java does)

Scripting Language: Instructions written to execute on runtime environment (like unix scripting enables with the deployment of web applications), JS is used with modifying DOM structure at the browser runtime.

Why so many programmers are not comfortable with JS by tagging it as a front end technology?
– Its because of the above traits of the language.
– Because of backward compatibility lot of bugs remained as bugs forever in JS (like == vs === , null typeof object, so on)
– Initially when it was introduced, it was meant to be friendly language and the hence it internally did lot of type coercions

Why learn JS? With NodsJS, Javascript evolved a lot and now it is being used widely across different layers

Client side web development

Native JS

JQuery

Angular, React

Server side

NodeJS

Express

Browser Extensions
so on..

Javascript runtime is usually a browser but as we learn this we can either use nodejs or mozilla firefox’s scratchpad to write and execute JS programs.